Fig. 7: Tectonic resides at the transition zone where it may act as a diffusional gate to ensure proper sorting of membrane proteins.

Model depicting tectonic’s proposed role in wildtype photoreceptors to prevent non-ciliary membrane proteins from infiltrating into the ciliary outer segment compartment. In Tctn1^-/- photoreceptors, the tectonic complex as well as components of the Mks and inner scaffold complex are downregulated. While this does not lead to gross structural defects in the transition zone or ciliary transport carriers, increased diffusion through the transition zone leads to non-ciliary membrane proteins, such as Stx3, becoming enriched in the enclosed membrane discs of the outer segment over time.